设计模式之代理模式

作用

为其他对象提供一种代理以控制对这个对象的访问。

静态代理

接口

public interface IBuyTicket {

    void buy(int price);

}

被代理对象

public class BuyTicket implements IBuyTicket {

    @Override
    public void buy(int price) {
        System.out.println("真实购票..." + price);
    }

}

代理对象

public class BuyTicketProxy implements IBuyTicket {

    private IBuyTicket iBuyTicket;

    public BuyTicketProxy(IBuyTicket iBuyTicket) {
        this.iBuyTicket = iBuyTicket;
    }

    @Override
    public void buy(int price) {
        System.out.println("代理购票开始");
        iBuyTicket.buy(price);
        System.out.println("代理购票结束");
    }
}

调用

public class Client {

    public static void main(String[] args) {
        IBuyTicket iBuyTicket = new BuyTicketProxy(new BuyTicket());
        iBuyTicket.buy(100);
    }

}

动态代理

也叫JDK代理或接口代理。

接口

public interface IBuyTicket {

    String buy(int price);

}

被代理对象

public class BuyTicket implements IBuyTicket {
    @Override
    public String buy(int price) {
        return "购买成功：票价100";
    }
}

代理工厂

public class ProxyFactory {

    private Object target;

    public ProxyFactory(Object target) {
        this.target = target;
    }

    public Object getProxyInstance() {
        /*return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                System.out.println("JDK代理开始");
                Object invoke = method.invoke(target, args);
                System.out.println("JDK代理结束");
                return invoke;
            }
        });*/
        return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), (proxy, method, args) -> {
            System.out.println("JDK代理开始");
            Object invoke = method.invoke(target, args);
            System.out.println("JDK代理结束");
            return invoke;
        });
    }
}

调用

public class Client {
    public static void main(String[] args) {
        ProxyFactory factory = new ProxyFactory(new BuyTicket());
        IBuyTicket proxyInstance = (IBuyTicket) factory.getProxyInstance();
        proxyInstance.buy(200);
    }
}

CGLIB代理

pom引用

<dependency>
    <groupId>cglib</groupId>
    <artifactId>cglib</artifactId>
    <version>3.3.0</version>
</dependency>

被代理对象

public class BuyTicket {

    public String buy() {
        return "Buy Success";
    }

}

代理工厂

public class ProxyFactory implements MethodInterceptor {

    private Object target;

    public ProxyFactory(Object target) {
        this.target = target;
    }

    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        System.out.println("cglib 开始");
        Object invoke = method.invoke(target, args);
        System.out.println("cglib 结束");
        return invoke;
    }

    public Object getInstance() {
        System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "./");
        //创建一个工具类
        Enhancer enhancer = new Enhancer();
        //设置父类
        enhancer.setSuperclass(target.getClass());
        //设置回调函数
        enhancer.setCallback(this);
        //创建子类对象，即代理对象
        return enhancer.create();
    }
}

调用

public class Client {

    public static void main(String[] args) {
        ProxyFactory proxyFactory = new ProxyFactory(new BuyTicket());
        BuyTicket buyTicket = (BuyTicket) proxyFactory.getInstance();
        buyTicket.buy();
    }

}

源码

org.springframework.cglib.proxy.MethodInterceptor